Lower vehicle-body structure

ABSTRACT

A lower vehicle-body structure comprises a vehicle floor comprising a bottom face portion and a floor tunnel, a pair of right-and-left first floor cross members extending in a vehicle width direction and provided on both sides of the floor tunnel, a pair of right-and-left second floor cross members extending in the vehicle width direction and provided on both sides of the floor tunnel, the second floor cross members being spaced rearwardly from the first floor cross members, a first connecting member provided to extend in the vehicle width direction at a position overlapping the first floor cross members in the vehicle longitudinal direction, and a second connecting member provided to extend in the vehicle width direction at a position overlapping the second floor cross members in the vehicle longitudinal direction.

BACKGROUND OF THE INVENTION

The present invention relates to a lower vehicle-body structure.

In an automotive vehicle, such as a FR (front-engine rear-drive) or 4WD(four-wheel drive) type of vehicle, a propeller shaft extending in avehicle longitudinal direction is provided in a power transmission paththrough which a power of a drive source is transmitted to driven wheels.The propeller shaft is generally arranged inside a floor tunnel which isprovided at a central portion, in a vehicle width direction, of avehicle floor. Further, in a vehicle equipped with a so-calledlongitudinally-disposed type of powertrain, for example, at least a partof a transmission is arranged inside the floor tunnel.

Meanwhile, a floor cross member which extends in the vehicle widthdirection is provided at an upper face of the vehicle floor forimproving the rigidity of a vehicle body and the like. In the vehiclebody provided with the above-described floor tunnel, the above-describedfloor cross member is configured as a pair of right-and-left floor crossmembers which are provided on both sides of the floor tunnel.

As disclosed in Japanese Patent Laid-Open Publication No. 2013-154731, apower transmission mechanism, such as the propeller shaft and thetransmission, which is provided inside the floor tunnel is supported bya mount member which is arranged below the power transmission mechanism.

In a vehicle-body structure disclosed in the above-described patentdocument, both end portions, in the vehicle width direction, of themount member are fixed to a lower face of the floor tunnel via areinforcing member (tunnel cross member) which is provided inside thefloor tunnel to cross over the propeller shaft. In this vehicle-bodystructure, a pair of right-and-left cross members provided on the bothsides of the floor tunnel are interconnected via the mount member andthe reinforcing member, whereby the vehicle-body rigidity is effectivelyimproved.

However, the structure disclosed in the above-described patent documentwhere the mount member is attached to the vehicle floor is insufficientfor properly improving the rigidity of the vehicle floor, and thereforean improved frame structure which considers a longitudinal frame and thelike, in addition to the floor cross members provided at the vehiclefloor, becomes necessary.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a lowervehicle-body structure which can properly improve the vehicle-bodyrigidity.

The present invention is a lower vehicle-body structure which comprise avehicle floor comprising a bottom face portion and a floor tunnel whichprotrudes upwardly and extends in a vehicle longitudinal direction, apair of right-and-left first floor cross members extending in a vehiclewidth direction and provided on both sides, in the vehicle widthdirection, of the floor tunnel, a pair of right-and-left second floorcross members extending in the vehicle width direction and provided onboth sides, in the vehicle width direction, of the floor tunnel, thesecond floor cross members being spaced rearwardly from the first floorcross members, a first connecting member provided to extend in thevehicle width direction at a position which overlaps the first floorcross members in the vehicle longitudinal direction and be fixed to thevehicle floor, and a second connecting member provided to extend in thevehicle width direction at a position which overlaps the second floorcross members in the vehicle longitudinal direction and be fixed to thevehicle floor, wherein the vehicle floor comprises a pair ofright-and-left upper step portions which are provided on both sides, inthe vehicle width direction, of the floor tunnel and configured to risetoward the floor tunnel from the bottom face portion, and the firstconnecting member and the second connecting member are fixed to theupper step portions.

According to the present invention, since a ladder-shaped structurewhich extends in the vehicle width direction, straddling the floortunnel, is formed at the vehicle floor by the first floor cross members,the second floor cross members, the first connecting member, and thesecond connecting member which respectively extend in the vehicle widthdirection and the upper step portions which extend in the vehiclelongitudinal direction, the vehicle-body rigidity can be properlyimproved.

Further, since the upper step portion configured to rise upwardly isprovided between the vehicle floor and the floor tunnel, the rigidity ofa boundary area between the vehicle floor and the floor tunnel can beproperly improved. Moreover, since the first connecting member and thesecond connecting member are fixed to the upper step portions, thevehicle-body rigidity can be properly improved.

In an embodiment of the present invention, the lower vehicle-bodystructure further comprises a pair of right-and-left floor framesextending in the vehicle longitudinal direction and provided on bothsides, in the vehicle width direction, of the floor tunnel, wherein thefloor frames are provided at a position which overlaps the first floorcross members and the second floor cross members in a vehicle verticaldirection.

According to this embodiment, since a ladder-shaped structure whichextends in the vehicle width direction, straddling the floor tunnel, isformed at the vehicle floor by the first floor cross members, the secondfloor cross members, the first connecting member, and the secondconnecting member which respectively extend in the vehicle widthdirection and the upper step portions and the floor frames whichrespectively extend in the vehicle longitudinal direction, thevehicle-body rigidity can be properly improved.

In another embodiment of the present invention, the lower vehicle-bodystructure further comprises a pair of right-and-left side sillsextending in the vehicle longitudinal direction and provided on bothsides, in the vehicle width direction, of the floor tunnel, wherein theside sills are provided at a position which overlaps the first floorcross members and the second floor cross members in a vehicle verticaldirection.

According to this embodiment, since a ladder-shaped structure whichextends in the vehicle width direction, straddling the floor tunnel, isformed at the vehicle floor by the first floor cross members, the secondfloor cross members, the first connecting member, and the secondconnecting member which respectively extend in the vehicle widthdirection and the upper step portions, the floor frames, and the sidesills which respectively extend in the longitudinal direction, thevehicle-body rigidity can be properly improved.

In another embodiment of the present invention, the above-describedupper step portions of the vehicle floor are located at the same levelas respective upper face portions of the first floor cross members inthe vehicle vertical direction.

According to this embodiment, since the upper step portions where thefirst connecting member is fixed and the upper face portions of thefirst floor cross members are located at the same level in the vehiclevertical direction, the effective load transmission between the firstconnecting member and the upper face portions of the first floor crossmembers can be attained.

Other features, aspects, and advantages of the present invention willbecome apparent from the following description which refers to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a lower vehicle-body structureaccording to an embodiment of the present invention.

FIG. 2 is a plan view showing the lower vehicle-body structure accordingto the embodiment.

FIG. 3 is a bottom view showing the lower vehicle-body structureaccording to the embodiment.

FIG. 4 is a sectional view taken along line A-A of FIG. 2.

FIG. 5 is a partial enlarged sectional view of FIG. 4.

FIG. 6 is a sectional view taken along line B-B of FIG. 2.

FIG. 7 is a partial enlarged sectional view of FIG. 6.

FIG. 8 is a perspective view of a mount member according to theembodiment.

FIG. 9 is a side view of the mount member according to the embodiment.

FIG. 10 is a perspective view showing a surrounding area of the mountmember according to the embodiment.

FIG. 11 is an exploded perspective view showing the surrounding area ofthe mount member according to the embodiment.

FIG. 12 is a plan view showing a surrounding area of a seat railaccording to the embodiment.

FIG. 13 is a partial enlarged sectional view of a modified example ofthe embodiment, which is similar to FIG. 5.

FIG. 14 is a partial enlarged sectional view of the modified example ofthe embodiment, which is similar to FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, an embodiment of the present invention will be describedreferring to the attached drawings.

[Whole Structure]

FIG. 1 is a perspective view showing a lower vehicle-body structureaccording to the embodiment of the present invention. FIG. 2 is a planview showing the lower vehicle-body structure. FIG. 3 is a bottom viewshowing the lower vehicle-body structure. In the following description,a vehicle width direction, a vehicle longitudinal direction, and avehicle vertical direction of an automotive vehicle 1 which is providedwith the lower vehicle-body structure according to the presentembodiment are respectively referred to as an X direction, a Ydirection, and a Z direction.

Referring to FIG. 1, the automotive vehicle 1 provided with the lowervehicle-body structure according to the present embodiment comprises avehicle floor 2 which constitutes a floor face of a space of a cabin, apair of side sills 4 which extend in the Y direction along both-sideportions, in the X direction, of the vehicle floor 2, and a dash panel10 which is provided in front of the vehicle floor 2.

Each of the side sills 4 comprises a side sill inner 5 and a side sillouter (not illustrated). The side sill inner 5 is configured to have ahat-shaped cross section which is opened to an outward side in the Xdirection in a cross section perpendicular to the Y direction. The sidesill outer is configured to have a hat-shaped cross section which isopened to an inward side in the X direction in the cross sectionperpendicular to the Y direction. The side sill inner 5 and the sidesill outer are joined together such that a closed cross section which iscontinuous in the Y direction is formed therebetween.

The automotive vehicle 1 further comprises a pair of hinge pillars 11which rise from respective front end portions of the right-and-left sidesills 4 and extend in the Z direction, and the dash panel 10 is providedbetween the pair of hinge pillars 11. A cabin space and an engine arepartitioned from each other in the Y direction by the dash panel 10.

The vehicle floor 2 comprises a bottom face portion 3 and a floor tunnel50 which is configured to protrude upwardly, in the Z direction, fromthe bottom face portion 3 and extend in the Y direction. The floortunnel 50 is provided to extend in the Y direction at a central portion,in the X direction, of the vehicle floor 2. A shape of a cross sectionof the floor tunnel 50, when viewed from the Y direction, is U-shapedwhich is opened to a downward side of the Z direction.

A opening portion 50 a for insertion of a shift lever (not illustrated)is formed at an upper face portion of the floor tunnel 50. A pair ofreinforcing members 8 which are configured to extend in the Y directionare joined to both-side portions, in the X direction, of the upper faceportion of the floor tunnel 50 by welding, for example, whereby therigidity of the floor tunnel 50 is increased.

A pair of right-and-left floor frames 12 which extend in the Y directionare joined to the bottom face portion 3 of the vehicle floor 2. Each ofthe floor frames 12 is provided between the floor tunnel 50 and the sidesill 4 in the X direction. In other words, each of the floor frames 12is provided on an inward side, in the X direction, of the side sill 4.The floor frame 12 is connected to a front end portion of the side sill4 via a torque box 22 (shown in FIG. 3).

The floor frame 12 comprises an upper frame member 61 which is joined toan upper face of the vehicle floor 2 by welding, for example, and alower frame member 62 which is joined to a lower face of the vehiclefloor 2 by welding, for example. The upper frame member 61 and the lowerframe member 62 are provided to face each other, interposing the vehiclefloor 2 therebetween. The upper frame member 61 and the lower framemember 62 are provided to extend in the Y direction, respectively. Thelower frame member 62 and the bottom face portion 3 of the vehicle floor2 jointly form a closed cross section which is continuous in the Ydirection. Referring to FIG. 2 as well, the upper frame member 61 of thepresent embodiment is provided between a second floor cross member 16,which will be described later, and the dash panel 10 in the Y direction.In other words, the upper frame member 61 is not provided on a rearwardside, in the Y direction, of the second floor cross member 16.

Referring to FIGS. 1 and 2, a pair of right-and-left first cross members14 and a pair of right-and-left second floor cross members 16 are joinedto the upper face of the bottom face portion 3 of the vehicle floor 2 asfloor cross members extending in the X direction, respectively. Thesecond floor cross members 16 are provided to be spaced apart,rearwardly in the Y direction, from the first floor cross members 14. Aninside seat rail 99 and an outside seat rail 100 are provided betweenthe first floor cross member 14 and the second floor cross member 16.

The first floor cross member 14 is provided to extend between the floortunnel 50 and the side sill 4. In other words, the right-and-left firstfloor cross members 14 are provided on both sides, in the X direction,of the floor tunnel 50. These both cross members 14 are arrangedsubstantially at the same position in the Y direction.

The first floor cross member 14 is a pressed part which is made ofsteel, for example, and configured to have a hat-shaped cross sectionwhich is opened downwardly in a cross section perpendicular to the Xdirection. The first floor cross member 14 and the vehicle floor 2jointly form a closed cross section which is continuous in the Xdirection. The first floor cross member 14 includes an upper faceportion 14 a which upwardly faces the bottom face portion 3 of thevehicle floor 2.

The upper face portion 14 a of the first floor cross member 14 isprovided to extend in the X direction. As shown in FIG. 2, a firstfront-side ridgeline L1 which extends in the X direction is formed at afront edge portion of the upper face portion 14 a, and a first rear-sideridgeline L2 which extends in the X direction is formed at a rear edgeportion of the upper face portion 14 a.

Referring to FIGS. 1 and 2, a first inside seat bracket 65 to supportthe inside seat rail 99 is joined to an inside end portion, in the Xdirection, of the first floor cross member 14. The first floor crossmember 14 is connected to the floor tunnel 50 via the first inside seatbracket 65. Further, a first outside seat bracket 66 is joined to anoutside end portion, in the X direction, of the first floor cross member14. The first floor cross member 14 is connected to the side sill 5 viathe first outside seat bracket 66. The first inside seat bracket 65 andthe first outside seat bracket 66 are respectively a pressed part madeof steel, for example.

The second floor cross member 16 is provided to extend between the floortunnel 50 and the side sill 4. In other words, the right-and-left firstfloor cross members 16 are provided on both sides, in the X direction,of the floor tunnel 50. These both cross members 16 are arrangedsubstantially at the same position in the Y direction.

The second floor cross member 16 is a pressed part which is made ofsteel, for example, and configured to have a hat-shaped cross sectionwhich is opened downwardly in a cross section perpendicular to the Xdirection. The second floor cross member 16 and the vehicle floor 2jointly form a closed cross section which is continuous in the Xdirection. The second floor cross member 16 includes an upper faceportion 16 a which upwardly faces the bottom face portion 3 of thevehicle floor 2.

The upper face portion 16 a of the second floor cross member 16 isprovided to extend in the X direction. As shown in FIG. 2, a secondfront-side ridgeline L3 which extends in the X direction is formed at afront edge portion of the upper face portion 16 a, and a secondrear-side ridgeline L4 which extends in the X direction is formed at arear edge portion of the upper face portion 16 a.

A connecting member 17 is joined to an inside end portion, in the Xdirection, of the second floor cross member 16 by welding, for example.The connecting member 17 is a pressed part made of steel, for example,and configured to have a hat-shaped cross section opened downwardly inthe cross section perpendicular to the X direction. The connectingmember 17 and the vehicle floor 2 jointly form a closed cross sectionwhich is continuous in the X direction. Further, the connecting member17 includes an upper face portion which extends in the X direction, andtwo ridgelines which are respectively continuous to the secondfront-side ridgeline L3 and the second rear-side ridgeline L4 of thesecond floor cross member 16 are formed at this upper face portion.Herein, the connecting member 17 may be formed integrally with thesecond floor cross member 16.

As shown in FIG. 2, a frame structure is formed at the vehicle floor 2by means of the first floor cross members 14 and the second floor crossmembers 16 which extend in the X direction and the floor frames 12 andthe side sills 4 which extend in the Y direction.

A second inside seat bracket 68 to support the inside seat rail 99 isjoined to the connecting member 17 joined to the inside end portion, inthe X direction, of the second floor cross member 16. The second floorcross member 16 is connected to the floor tunnel 50 via the secondinside seat bracket 68 and the connecting member 17. Further, a secondoutside seat bracket 69 is joined to an outside end portion, in the Xdirection, of the second floor cross member 16. The second floor crossmember 16 is connected to the side sill inner 5 via the second outsideseat bracket 69. The second inside seat bracket 68 and the secondoutside seat bracket 69 are respectively a pressed part made of steel,for example.

A pair of inside seat rails 99 are provided at both sides (right sideand left side), in the X direction, of the floor tunnel 50. Likewise, apair of outside seat rails 100 are provided at both sides (right sideand left side), in the X direction, of the floor tunnel 50. A pair offront seats (not illustrated) which are provided on the right-and-leftsides of the floor tunnel 50 are supported at the inside seat rails 99and the outside seat rails 100 from a downward side so as to slide inthe Y direction. Each of the inside seat rail 99 and each of the outsideseat rails 100 are provided to be spaced apart from each other in the Xdirection and extend in the Y direction. The inside seat rail 99 and theoutside seat rail 100 are respectively a pressed part made of steel, forexample, and configured to have a roughly C-shaped cross section whishis opened upwardly in the cross section perpendicular to the Ydirection.

The inside seat rail 99 is fixed to the first inside seat bracket 65 atits front end portion and fixed to the second inside seat bracket 68 atits rear end portion. The outside seat rail 100 is fixed to the firstoutside seat bracket 66 at its front end portion and fixed to the secondoutside seat bracket 69 at its rear end portion.

Further, a pair of right-and-left oblique frames 18 are joined to theupper face portion 3 of the vehicle floor 2 by welding, for example.This oblique frame 18 is provided to extend obliquely inwardly andrearwardly in front of the first floor cross member 14. The obliqueframe 18 is provided to interconnect the floor frame 12 and the sidesill 4. A connection portion of the oblique frame 18 to the side sill 4is provided to overlap the hinge pillar in the Y direction. The obliqueframe 18 is configured to have a hat-shaped cross section openeddownwardly in a cross section which is perpendicular to a longitudinaldirection of the oblique frame 18, and the oblique frame 18 and thevehicle floor 2 jointly form a closed cross section which is continuousin the longitudinal direction of the oblique frame 18.

Referring to FIG. 3, a mount member (first connecting member) 70 and atunnel member (second connecting member) 80 as connecting members arejoined to the lower face of the vehicle floor 2. The mount member 70 isprovided to extend in the X direction and located at a position whichcorresponds to the first floor cross member 14 in the Y direction. Thetunnel member 80 is provided to extend in the X direction and located ata position which corresponds to the second floor cross member 16 in theY direction.

Further, a ladder-shaped structure is formed at the vehicle floor 2 bymeans of the first floor cross members 14, the second floor cross member16, the mount member 70 and the tunnel member 80 which respectivelyextend in the X direction, and a pair of an upper step portions 51(described later), a pair of floor frames 12 and a pair of side sills 4which respectively extend in the Y direction. This ladder-shapedstructure is configured to extend in the X direction across the floortunnel 50.

Herein, as shown in FIG. 3, a pair of tunnel side reinforcements(reinforcing member) 81 which extend in the Y direction are provided atthe lower face of the vehicle floor 2. Each of the tunnel sidereinforcements 81 and the vehicle floor 2 jointly form a closed crosssection. Each of the tunnel side reinforcements 81 is located at aposition which overlaps the mount member 70 in the Y direction.

The automotive vehicle 1 provided with the lower vehicle-body structureof the present embodiment is a FR type of automotive vehicle equippedwith a longitudinally-disposed type of powertrain, for example. Thepowertrain of the present lower vehicle-body structure comprises anengine (not illustrated) as a power source which is installed in theengine room at a position located in front of the dash panel 10 (seeFIG. 1) and a transmission 24 which is rearwardly coupled to the engine.

The transmission 24 is a longitudinally-disposed type of automatictransmission, for example, and comprises an output shaft (notillustrated) which extends in the Y direction. However, thistransmission 24 may be a manual transmission. A rear end portion of theoutput shaft of the transmission 24 is coupled to a propeller shaft 30which extends in the Y direction via a flexible joint 28. Thus, a powerof the engine is transmittable to rear wheels through a powertransmitting mechanism, such as the transmission 24 and the propellershaft 30.

The propeller shaft 30 is disposed inside the floor tunnel 50. Thepropeller shaft 30 is supported at a lower face of the floor tunnel 50via a shaft bearing 32 and a support member 34.

At least a part of a rear-end side of the transmission 24 is disposedinside the floor tunnel 50 as well. A supported portion 26 which issupported by the mount member 70 (first connecting member) from andownward side of the floor panel 50 is provided at a rear end of thetransmission 24. This supported portion 26 is provided near the rear endportion of the transmission 24.

As described above, the mount member 70 is fixed to the vehicle floor 2at a position which overlaps the first floor cross member 14 in the Ydirection. Thus, a rear portion of the transmission 24 is supported at avehicle body via the mount member 70. Herein, a front portion of thetransmission 24 is supported at the vehicle body (a front suspensionmember, for example) via the engine and an engine mount (notillustrated). The mount member 70 and its fixation structure will bedescribed later.

[Surrounding Structure of Mount Member]

FIG. 4 is a sectional view taken along line A-A of FIG. 2. FIG. 5 is apartial enlarged sectional view of FIG. 4. Referring to FIGS. 4 and 5, aportion, in the Y direction, of the vehicle floor 2 where the mountmember 70 and the first floor cross member 14 are provided and itssurrounding area will be described.

As shown in FIG. 4, the vehicle floor 2 comprises a tunnel panel 40which constitutes the floor tunnel 50 and a pair of right-and-leftbottom face panels 42 which constitute the bottom face portion 3. Thetunnel panel 40 is provided at a central portion, in the X direction, ofthe vehicle floor 2 between the right-and-left side sills 4. Each of thebottom face panels 42 is provided to interconnect the tunnel panel 40and the side sill 4.

The tunnel panel 40 and the bottom face panel 42 are respectively apressed part made of steel, for example. It is preferable that thetunnel panel 40 have the higher rigidity and strength than the bottomface panel 42, whereby the rigidity and strength of the floor tunnel 50can be improved.

The vehicle floor 2 further includes a pair of upper step portions 51which are configured to rise inwardly, in the X direction, from thebottom face portion 3 and be continuous to a lower edge portion of thefloor tunnel 50. Referring to FIGS. 1 through 3, the upper step portion51 is configured to extend in the Y direction along the lower edgeportion of the floor tunnel 50 from a forward side of the first floorcross member 14 to a rearward side of the second floor cross member 16.Further, as shown in FIGS. 2 and 3, a ridgeline L5 is formed at theupper step portion 51. As shown in FIG. 3, the mount member 70 is fixedto the upper step portion 51.

Thus, the upper step portion 51 integrally formed with the vehicle floor2 is provided at a boundary area between the bottom face portion 3 andthe lower edge portion of the floor tunnel 50, whereby the rigidity isincreased.

Herein, referring to FIG. 3, the tunnel side reinforcement 81 isprovided along the boundary area of the bottom face portion 3 and thelower edge portion of the front tunnel 50. The tunnel side reinforcement81 is located at the position which overlaps the mount member 70 of theupper step portion 51.

Referring to FIG. 5, the upper step portion 51 comprises a first lateralplate portion 51 a which is configured to extend outwardly, in the Xdirection, from the lower end portion of the floor tunnel 50 and a firstslant portion 51 b which is configured to extend obliquely downwardly,in the Z direction, from an outside end portion, in the X direction, ofthe first lateral plate portion 51 a. Herein, the first slant portion 51b may be configured to extend downwardly, in the Z direction. The mountmember 70 is fixed to the first lateral plate portion 51 a of the upperstep portion 51.

In the present embodiment, the first lateral plate portion 51 a and thefirst slant portion 51 b of the upper step portion 51 are constituted bya part of the tunnel panel 40. The tunnel panel 40 further comprises anextension portion 51 c which extends outwardly, in the X direction, froma lower end portion of the first slant portion 51 b. The extensionportion 51 c is joined to the bottom face panel 42 by welding, forexample.

Herein, the upper step portion 51 may be configured by a part of thebottom face panel 42 or a different member from the tunnel panel 40 andthe bottom face panel 42.

Referring to FIG. 4, the bottom face portion 3 of the vehicle floor 2comprises a pair of right-and-left middle step portions 52 which arecontinuous to an outside portion, in the X direction, of the upper stepportion 51, a pair of right-and-left lower step portions 53 which arecontinuous to an outside portion, in the X direction, of the middle stepportion 52, and a joined portion 54 which is joined to the side sill 4on the outside, in the X direction, of the lower step portion 53.

Referring to FIG. 5, the middle step portion 52 comprises a secondlateral plate portion 52 a which is configured to extend in the Xdirection and a second slant portion 52 b which is configured to extendobliquely outwardly, in the X direction, and downwardly, in the Zdirection, from an outside end portion of the second lateral plateportion 52 a. Further, the middle step portion 52 comprises a thirdlateral plate portion 52 c which is configured to extend outwardly, inthe X direction, from an outside end portion, in the X direction, of thesecond slant portion 52 c and a third slant portion 52 d which isconfigured to extend obliquely outwardly, in the X direction, anddownwardly, in the Z direction, from an outside end portion of the thirdlateral plate portion 52 c. The second lateral plate portion 52 a of themiddle step portion 52 is joined to an upper face of the extensionportion 51 c of the tunnel panel 40. Thus, an inside end portion, in theX direction, of the second lateral plate portion 52 a of the middle stepportion 52 is connected to a lower end portion of the first slantportion 51 b of the upper step portion 51 via the extension portion 51c.

The upper frame member 61 and the lower frame member 62 which constitutethe floor frame 12 are provided to face each other, interposing thethird lateral plate portion 52 c and the third slant portion 52 d of themiddle step portion 52 therebetween.

The lower step portion 53 comprises a fourth lateral plate portion 53 awhich extends outwardly, in the X direction, from a lower end portion ofthe third slant portion 52 d of the middle step portion 52. The fourthlateral plate portion 53 a of the lower step portion 53 constitutes alowermost part of the vehicle floor 2.

The upper frame member 61 and the lower frame member 62 of the floorframe 12 are joined to the third lateral plate portion 52 c of themiddle step portion 52 and the fourth lateral plate portion 53 a of thelower step portion 53 by welding, whereby the members 61, 62 are fixedto the bottom face panel 42.

Referring to FIG. 4, the joined portion 54 is provided to extendupwardly from an outside end portion, in the X direction, of the lowerstep portion 53. The joined portion 54 is joined to a cabin-side face ofthe side sill inner 5 of the side sill 4 by welding, for example.

Thus, the lower step portion 53 is located at a lower level than thejoined portion 54 joined to the side sill 4 in the Z direction.Accordingly, a sectional area of the closed cross section formed betweenthe vehicle floor 2 and the first floor cross member 14 is enlarged inan area of the X direction where the lower step portion 53 is provided,so that the rigidity improvement of the first floor cross member 14 isattained.

Herein, the sectional shape of the vehicle floor 2 taken along line A-Aof FIG. 2 is not limited to the structure shown in FIGS. 4 and 5 butchangeable. For example, the middle step portion 52 provided between theupper step portion 51 and the lower step portion 53 may be formed in onestage or three or more stages, or may be omitted. Further, while thelower step portion 53 is located at the lower level than the joinedportion 54 in the present embodiment, the fourth lateral plate portion53 a of the lower step portion 53 may be located at a level whichoverlaps the joined portion 54 or at a higher level than the joinedportion 54.

As shown in FIG. 5, the upper face portion 14 a of the first floor crossmember 14 with the first front-side ridgeline L1 and the first rear-sideridgeline L2 (see FIGS. 1 and 2) is located at a higher level than themiddle step portion 52 and the lower step portion 53 of the vehiclefloor 2 and also substantially at the same level as the first lateralplate portion 51 a of the upper step portion 51.

Further, as shown in FIG. 4, the floor frame 12, the first floor crossmember 14, and the side sill 4 are positioned such that these overlap inthe Z direction.

Referring to FIGS. 4 and 5, the first inside seat bracket 65 is joinedto an outside face of the floor tunnel 50 by welding, for example, at aninside end portion, in the X direction, thereof. As shown the mostapparently in FIG. 5, an outside end portion, in the X direction, of thefirst inside seat bracket 65 is jointly fastened with the first floorcross member 14, the first lateral plate portion 51 a of the upper stepportion 51, and the mount member 70. Thereby, the first floor crossmember 14 is connected to the floor tunnel 50 via the first inside seatbracket 65.

Referring to FIG. 4, an inside end portion, in the X direction, of thefirst outside seat bracket 66 is joined to the upper face portion 14 aof the first floor cross member 14 by welding, for example. An outsideend portion, in the X direction, of the first outside seat bracket 66 isjoined to the inside face of the side sill inner 5 of the side sill 4 bywelding, for example.

[Surrounding Structure of Tunnel Member]

FIG. 6 is a sectional view taken along line B-B of FIG. 2. FIG. 7 is apartial enlarged sectional view of FIG. 6. Referring FIGS. 6 and 7, aportion, in the Y direction, of the vehicle floor 2 where the tunnelmember 80 and the second floor cross member 16 are provided and itssurrounding arear will be described. The cross section of the vehiclefloor 2 shown in FIGS. 6 and 7 is similar to the cross section of thevehicle floor 2, specific description of which is omitted here.

Referring to FIG. 6, the tunnel member 80 is fixed to the upper stepportion 51. More specifically, the tunnel member 80 is fixed to a lowerface of the first lateral plate portion 51 a of the upper step portion51 as shown in FIG. 7.

Referring to FIGS. 6 and 7, the connecting member 17 is joined to theinside end portion, in the X direction, of the second floor cross member16 as described above. The inside end portion, in the X direction, ofthe connecting member 17 is fixed to the first lateral plate portion 51a of the upper step portion 51 and the tunnel member 80, whereby theupper step portion 16 a of the second floor cross member 16 is connectedto the first lateral plate portion 51 a of the upper step portion 51.Herein, the connecting member 17 may be formed integrally with thesecond floor cross member 16.

Since the upper frame member 61 is provided on the forward side, in theY direction, of the second floor cross member 16 as described above (seeFIG. 2), the upper frame member 61 which constitutes the floor frame 12is not provided in the cross section shown in FIGS. 6 and 7. The closedcross section is formed by the bottom face panel 42 and the lower framemember 62.

As shown in FIG. 7, the upper face portion 16 a of the second floorcross member 16 with the second front-side ridgeline L3 and the secondrear-side ridgeline L4 (see FIGS. 1 and 2) is located at a higher levelthan the middle step portion 52 and the lower step portion 53 of thevehicle floor 2 and also substantially at the same level as the firstlateral plate portion 51 a of the upper step portion 51.

The second inside seat bracket 68 is joined to the outside face of thefloor tunnel 50 by welding, for example, at an inside end portion, inthe X direction, thereof, and connected to the connecting member 17 bywelding, for example, at an outside end portion, in the X direction,thereof. Thereby, the second floor cross member 16 is connected to thefloor tunnel 50 via the second inside seat bracket 68 and the connectingmember 17.

As shown in FIG. 6, an inside end portion, in the X direction, of thesecond outside seat bracket 69 is joined to the upper face portion 16 aof the second floor cross member 16 by welding, for example. An outsideend portion, in the X direction, of the second outside seat bracket 69is joined to the inside face of the side sill inner 5 of the side sill 4by welding, for example.

Referring to FIG. 6, the floor frame 12, the first floor cross member14, the second floor cross member 16, and the side sill 4 are providedsuch that these overlap in the Z direction. That is, a frame-shapedstructure which is formed, at the vehicle floor 2, by the floor frame 12and the side sill 4 which respectively extend in the Y direction and thefirst floor cross member 14 and the second floor cross member 16 whichrespectively extend in the X direction is configured such that it is notoffset in the Z direction.

[Mount Member]

FIG. 8 is a perspective view of the mount member 70 according to thepresent embodiment. FIG. 9 is a side view of the mount member 70 of thepresent embodiment, when viewed from a right side in the X direction, ofthe vehicle body. A structure of the mount member 70 will be describedreferring to FIGS. 8 and 9. In FIGS. 8 and 9, the vehicle widthdirection, the vehicle longitudinal direction, and the vehicle verticaldirection in a case where the mount member 70 is attached to the vehiclefloor 2 (see FIG. 3) are shown as the X direction, the Y direction, andthe Z direction, respectively.

Referring to FIG. 8, the mount member 70 is a casting part made ofaluminum alloy, for example. The mount member 70 comprises a base part71 which extends in the X direction and a fixation part 72 which isprovided at both end portions, in the X direction, of the base part 71.

The base part 71 is configured to protrude downwardly in the Zdirection, which is of a curved shape, when viewed from the Y direction.The transmission 24 (shown in FIG. 3) is supported at the vehicle floor2 (shown in FIG. 3) via the base part 71 of the mount member 70.

Each of the fixation parts 72 comprises a first protrusion portion 73which is provided at a central portion, in the Y direction, of the basepart 71, a second protrusion portion 74 which is provided to beforwardly spaced, in the Y direction, apart from the first protrusionportion 73, and a third protrusion portion 75 which is provided to berearwardly spaced, in the Y direction, apart from the first protrusionportion 73.

The first protrusion portion 73 is configured to protrude outwardly, inthe X direction, from the base part 71. The first protrusion portion 73includes an outside fixation point 73 a and an inside fixation point 73b, where the mount member 70 is fixed to the vehicle floor 2.

The outside fixation point 73 a is positioned at an outside end portion,in the X direction, of the first protrusion portion 73. The outsidefixation point 73 a has a through (penetration) hole where the firstprotrusion portion 73 is inserted in the Z direction.

The inside fixation point 73 b is provided to be spaced, in the Xdirection, apart from the outside fixation point 73 a. A through holewhere the first protrusion portion 73 is inserted in the Z direction isformed at the inside fixation point 73 b. The inside fixation point 73 bis located substantially at the same level, in the Z direction, as theoutside fixation point 73 a.

The second protrusion portion 74 is configured to protrude outwardly, inthe X direction, and forwardly, in the Y direction, from the base part71. An outside end portion, in the X direction, of the second protrusionportion 74 has a fixation point 74 a where the mount member 70 is fixedto the vehicle floor 2. This fixation point 74 a has a through holewhere the second protrusion portion 74 is inserted in the Z direction.

The third protrusion portion 75 is configured to protrude outwardly, inthe X direction, and rearwardly, in the Y direction, from the base part71. An outside end portion, in the X direction, of the third protrusionportion 75 has a fixation point 75 a where the mount member 70 is fixedto the vehicle floor 2. This fixation point 75 a has a through holewhere the third protrusion portion 75 is inserted in the Z direction.

As shown in FIG. 9, the outside fixation point 73 a of the firstprotrusion portion 73, the fixation point 74 a of the second protrusionportion 74, and the fixation point 75 a of the third protrusion portion75 are located at different levels, in the Z direction, from each otherin a state where the mount member 70 is attached to the vehicle floor 2(shown in FIG. 3). Specifically, the outside fixation point 73 a of thefirst protrusion portion 73 is located a higher level than the fixationpoint 74 a of the second protrusion portion 74 and the fixation point 75a of the third protrusion portion 75. Herein, since the inside fixationpoint 73 b (shown in FIG. 8) of the first protrusion portion 73 islocated substantially at the same level, in the Z direction, as theoutside fixation point 73 a as described above, this point 73 b isprovided on an upward side, in the Z direction, of the fixation point 74a of the second protrusion portion 74 and the fixation point 75 a of thethird protrusion portion 75.

The fixation point 74 a of the second protrusion portion 74 and thefixation point 75 a of the third fixation portion 75 are locatedsubstantially at the same position in the Z direction.

[Attachment Structure of Mount Member]

FIG. 10 is a perspective view showing a surrounding arear of the mountmember 70. FIG. 11 is an exploded perspective view showing thesurrounding area of the mount member 70. An attachment structure of themount member 70 to the vehicle floor 2 will be described referring toFIGS. 10 and 11.

Referring to FIG. 10, the mount member 70 is fixed to the vehicle floor2 at plural (four, in the present embodiment) fixation positions P1, P2,P3, P4 at both sides, in the X direction, thereof. Plural bolts are usedfor attachment of the mount member 70 to the vehicle floor 2. Further,the mount member 70 is attached to the vehicle floor directly or via thetunnel side reinforcements 81.

Referring to FIG. 11, at the first lateral plate portion 51 a of theupper step portion 51 of the vehicle floor 2 are formed through holeswhich respectively correspond to the outside fixation portion 73 a andthe inside fixation point 73 b of the first protrusion portion 73 of themount member 70. Further, a through hole which corresponds to thefixation portion 74 a of the second protrusion portion 74 of the mountmember 70 and a through hole which corresponds to the fixation portion75 a of the third protrusion portion 75 of the mount member 70 areformed at the first lateral plate portion 51 a of the upper step portion51 of the vehicle floor 2.

The tunnel side reinforcement 81 is attached to the first lateral plateportion 51 a of the upper step portion 51 as described above. The tunnelside reinforcement 81, which extends in the Y direction, comprises afirst attachment portion 81 a which corresponds to the first protrusionportion 73 of the mount member 70, a second attachment portion 81 bwhich corresponds to the second protrusion portion 74 of the mountmember 70, and a third attachment portion 81 c which corresponds to thethird protrusion portion 75.

The first attachment portion 81 a of the tunnel side reinforcement 81 isa flat-plate shaped part which extends along the first lateral plateportion 51 a of the upper step portion 51, and a through hole (notillustrated) is formed at a position which corresponds to the insidefixation point 73 b of the first protrusion portion 73.

The second attachment portion 81 b of the tunnel side reinforcement 81is configured to protrude downwardly, in the Z direction, so as to forma closed cross section together with the first lateral plate portion 51a of the upper step portion 51. A through hole (not illustrated) isformed at the second attachment portion 81 b of the tunnel sidereinforcement 81 at a position corresponding to the fixation point 74 aof the second protrusion portion 74.

The third attachment portion 81 c of the tunnel side reinforcement 81 isconfigured to protrude downwardly, in the Z direction, so as to form aclosed cross section together with the first lateral plate portion 51 aof the upper step portion 51. A through hole (not illustrated) is formedat the third attachment portion 81 c of the tunnel side reinforcement 81at a position corresponding to the fixation point 75 a of the thirdprotrusion portion 75.

Referring to FIG. 9, the mount member 70 is fixed to the first lateralplate portion 51 a of the upper step portion 51 at the outside fixationpoint 73 a of the first protrusion portion 73 (the fixation position P1of FIG. 10) and also fixed to the first attachment portion 81 a of thetunnel side reinforcement 81 at the inside fixation point 73 b (shown inFIG. 8) of the first protrusion portion 73 (the fixation position P4 ofFIG. 10). Further, the mount member 70 is fixed to the second lateralplate portion 81 b of the tunnel side reinforcement 81 at the fixationpoint 74 a of the second protrusion portion 74 (the fixation position P2of FIG. 10) and also fixed to the third attachment portion 81 c of thetunnel side reinforcement 81 at the fixation point 75 a of the thirdprotrusion portion 75 (the fixation position P3 of FIG. 10). As apparentfrom FIG. 9, the second attachment portion 81 b and the third attachmentportion 81 c of the tunnel side reinforcement 81 are positioned on thedownward side, in the Z direction, of the first lateral plate portion 51a of the upper step portion 51.

In other words, the fixation positions P1, P2, P3, P4 of the mountmember 70 to the vehicle floor 2 are set at different positions, in theZ direction, from each other.

Further, in the three fixation positions P1, P2, P3 which are arrangedin the Y direction, the fixation position P1 which is located at acenter, in the Y direction, of three positions is provided at the firstlateral plate portion 51 a of the upper step portion 51, and the othertwo fixation positions P2, P3 are provided at the tunnel sidereinforcement 81. That is, the central fixation position P1, in the Ydirection, is provided to overlap the upper face portion 14 a of thefirst floor cross member 14 in the Z direction (see FIG. 4).

Further, referring to FIG. 4, the fixation part 72 of the mount member70 is positioned in a range of a height, in the Z direction, of thefirst floor cross member 14. That is, the four fixation positions P1,P2, P3, P4 of the mount member 70 to vehicle floor 2 are positioned inthe range of the height, in the Z direction, of the first floor crossmember 14.

[Tunnel Member]

Referring to FIGS. 6 and 10, the tunnel member 80 is a hollow extrudedone which is configured to extend in the X direction and have a closedcross section in the cross section perpendicular to the X direction. Thetunnel member 80 is made of aluminum alloy, for example. The tunnelmember 80 is fixed to the first lateral plate portions 51 a of the upperstep portions 51 at both end portion, in the X direction, thereof. Asshown in FIG. 6, the tunnel member 80 is located in a rage of a height,in the Z direction, of the second floor cross member 16. Specifically,the tunnel member 80 is positioned in the Z direction so that itoverlaps the upper face portion 16 a of the second floor cross member16.

[Surrounding Structure of Inside Seat Rail]

FIG. 12 is a plan view showing a surrounding area of the inside seatrail 99 and the outside seat rail 100. Referring to FIGS. 1, 4, 6 and12, a structure of the side sill 4 around the inside seat rail 99 willbe described.

Referring to FIG. 1, the side sill 4 of the present embodiment hasplural (five in the present embodiment) gussets 101 which are providedinside the side sill inner 5.

The gusset 101 is a flat-plate shaped member which extends along a planecrossing the Y direction, and fixed to the side sill inner 5 by welding,for example. As apparently shown in FIG. 12, a gusset 101A is located ata position which overlaps the first floor cross member 14 in the Ydirection. Specifically, the gusset 101A is provided on the side of thesecond floor cross member 16 of a center of the first floor cross member14 in the Y direction at a position which overlaps the first rear-sideridgeline L2. Further, a gusset 101B is located at a position whichoverlaps the second floor cross member 16 in the Y direction.Specifically, the gusset 101B is provided on the side of the first floorcross member 14 of a center of the second floor cross member 16 in the Ydirection at a position which overlaps the second front-side ridgelineL3.

Referring to FIG. 4, the gusset 101 is provided such that it overlapsthe first floor cross member 14 ad the floor frame 12 in the Zdirection. Referring to FIG. 6, the gusset 101 is provided such that itoverlaps the second floor cross member 16 ad the floor frame 12 in the Zdirection.

Referring to FIG. 12, as described above, the ladder-shaped structure isformed by means of the first floor cross members 14 and the second floorcross member 16 which respectively extend in the X direction and theupper step portions 51, the floor frames 12, and the side sills 4 whichrespectively extend in the Y direction. The first inside seat bracket65, the outside seat bracket 66, the second inside seat bracket 68, andthe second outside seat bracket 69 are fixed to the above-describedladder-shaped structure. That is, the inside seat rail 99 and theoutside seat rail 100 are fixed to the ladder-shaped structure.

According to this structure, since the ladder-shaped structure whichextends in the X direction, straddling the floor tunnel 50, is formed atthe vehicle floor 2 by the first floor cross members 14, the secondfloor cross members 16, the mount member 70, and the tunnel member 80which respectively extend in the X direction and the upper step portions51 (ridgelines L5), the floor frames 12, and the side sills 4 whichextend in the Y direction, the vehicle-body rigidity can be properlyimproved.

Further, since the upper step portion 51 configured to rise is providedbetween the vehicle floor 2 and the floor tunnel 50, the rigidity of aboundary area between the vehicle floor 2 and the floor tunnel 50 can beproperly improved. Moreover, since the mount member 70 and the tunnelmember 80 are fixed to the upper step portions 51, the vehicle-bodyrigidity can be properly improved.

Additionally, since the first lateral plate portions 51 a of the upperstep portions 51 of the vehicle floor 2 where the mount member 70 isfixed and the upper face portions 14 a of the first floor cross members14 are located at the same level in the Z direction, the effective loadtransmission between the mount member 70 and the upper face portions 14a of the first floor cross members 14 can be attained.

Modified Example

Referring to FIGS. 13 and 14, a modified example of the fixationstructure of the inside seat rail 99 will be described.

Referring to FIG. 13, the inside seat rail 99 of the modified example isfastened together with the first inside seat bracket 65, the upper stepportion 51, and the mount member 70. Specifically, a tall nut (spacermember) 91 is provided to penetrate the mount member 70 and the firstlateral plate portion 51 a of the upper step portion 51, and a bolt 92which is provided to penetrate the first inside seat bracket 65 and theinside seat rail 99 is screwed to the tall nut 91.

Further, referring to FIG. 14, the inside seat rail 99 of the modifiedexample is fastened together with the second inside seat bracket 68, theupper step portion 51, and the connecting member 17. Specifically, atall nut (spacer member) 93 is provided to penetrate the connectingmember 17 and the first lateral plate portion 51 a of the upper stepportion 51, and a bolt 94 which is provided to penetrate the secondinside seat bracket 68 and the inside seat rail 99 is screwed to thetall nut 93.

The present invention should not be limited to the above-describedembodiment and modified example and any other modifications orimprovements may be applied within the scope of a spirit of the presentinvention.

For example, while the tall nut 91 is used as the spacer member which isprovided between the vehicle floor 2 and the first inside seat bracket65 according to the above-described modified example, a collar having noscrew hole may be applied instead of the spacer member in the presentinvention.

What is claimed is:
 1. A lower vehicle-body structure, comprising: avehicle floor comprising a bottom face portion and a floor tunnel whichprotrudes upwardly and extends in a vehicle longitudinal direction; apair of right-and-left first floor cross members extending in a vehiclewidth direction and provided on both sides, in the vehicle widthdirection, of the floor tunnel; a pair of right-and-left second floorcross members extending in the vehicle width direction and provided onboth sides, in the vehicle width direction, of the floor tunnel, thesecond floor cross members being spaced rearwardly from the first floorcross members; a first connecting member provided to extend in thevehicle width direction at a position which overlaps the first floorcross members in the vehicle longitudinal direction and be fixed to thevehicle floor; and a second connecting member provided to extend in thevehicle width direction at a position which overlaps the second floorcross members in the vehicle longitudinal direction and be fixed to thevehicle floor, wherein said vehicle floor comprises a pair ofright-and-left upper step portions which are provided on both sides, inthe vehicle width direction, of the floor tunnel and configured to risetoward said floor tunnel from said bottom face portion, and said firstconnecting member and said second connecting member are directly fixedto said upper step portions on a first side of the right-and-left upperstep portions and each of the pair of right-and-left first floor crossmembers and each of the pair of right-and-left second floor crossmembers is directly fixed to said upper step portions on a second,opposite side of the right-and-left upper step portions from said firstconnecting member and said second connecting member.
 2. The lowervehicle-body structure of claim 1, further comprising a pair ofright-and-left floor frames extending in the vehicle longitudinaldirection and provided on both sides, in the vehicle width direction, ofsaid floor tunnel, wherein said floor frames are provided at a positionwhich overlaps said first floor cross members and said second floorcross members in a vehicle vertical direction.
 3. The lower vehicle-bodystructure of claim 2, wherein further comprising a pair ofright-and-left side sills extending in the vehicle longitudinaldirection and provided on both sides, in the vehicle width direction, ofsaid floor tunnel, wherein said side sills are provided at a positionwhich overlaps said first floor cross members and said second floorcross members in the vehicle vertical direction.
 4. The lowervehicle-body structure of claim 3, wherein said upper step portions ofthe vehicle floor contact a lower surface of respective upper faceportions of said first floor cross members in the vehicle verticaldirection.
 5. The lower vehicle-body structure of claim 2, wherein saidupper step portions of the vehicle floor contact a lower surface ofrespective upper face portions of said first floor cross members in thevehicle vertical direction.
 6. The lower vehicle-body structure of claim1, wherein further comprising a pair of right-and-left side sillsextending in the vehicle longitudinal direction and provided on bothsides, in the vehicle width direction, of said floor tunnel, whereinsaid side sills are provided at a position which overlaps said firstfloor cross members and said second floor cross members in a vehiclevertical direction.
 7. The lower vehicle-body structure of claim 6,wherein said upper step portions of the vehicle floor contact a lowersurface of respective upper face portions of said first floor crossmembers in the vehicle vertical direction.
 8. The lower vehicle-bodystructure of claim 1, wherein said upper step portions of the vehiclefloor contact a lower surface of respective upper face portions of saidfirst floor cross members in a vehicle vertical direction.
 9. The lowervehicle-body structure of claim 1, wherein said first connecting memberis directly fixed to said upper step portions, said first connectingmember forming a curved downward concave shape at a location betweensaid pair of right-and-left upper step portions.
 10. A lowervehicle-body structure, comprising: a vehicle floor comprising a bottomface portion and a floor tunnel which protrudes upwardly and extends ina vehicle longitudinal direction; a pair of right-and-left first floorcross members extending in a vehicle width direction and provided onboth sides, in the vehicle width direction, of the floor tunnel; a pairof right-and-left second floor cross members extending in the vehiclewidth direction and provided on both sides, in the vehicle widthdirection, of the floor tunnel, the second floor cross members beingspaced rearwardly from the first floor cross members; a first connectingmember provided to extend in the vehicle width direction at a positionwhich overlaps the first floor cross members in the vehicle longitudinaldirection and be fixed to the vehicle floor; and a second connectingmember provided to extend in the vehicle width direction at a positionwhich overlaps the second floor cross members in the vehiclelongitudinal direction and be fixed to the vehicle floor, wherein saidvehicle floor comprises a pair of right-and-left upper step portionswhich are provided on both sides, in the vehicle width direction, of thefloor tunnel and configured to rise toward said floor tunnel from saidbottom face portion, and said first connecting member is directly fixedto said upper step portions, said first connecting member forming acurved downward concave shape at a location between said pair ofright-and-left upper step portions.
 11. The lower vehicle-body structureof claim 10, further comprising a pair of right-and-left floor framesextending in the vehicle longitudinal direction and provided on bothsides, in the vehicle width direction, of said floor tunnel, whereinsaid floor frames are provided at a position which overlaps said firstfloor cross members and said second floor cross members in a vehiclevertical direction.
 12. The lower vehicle-body structure of claim 11,wherein further comprising a pair of right-and-left side sills extendingin the vehicle longitudinal direction and provided on both sides, in thevehicle width direction, of said floor tunnel, wherein said side sillsare provided at a position which overlaps said first floor cross membersand said second floor cross members in the vehicle vertical direction.13. The lower vehicle-body structure of claim 12, wherein said upperstep portions of the vehicle floor contact a lower surface of respectiveupper face portions of said first floor cross members in the vehiclevertical direction.
 14. The lower vehicle-body structure of claim 11,wherein said upper step portions of the vehicle floor contact a lowersurface of respective upper face portions of said first floor crossmembers in the vehicle vertical direction.
 15. The lower vehicle-bodystructure of claim 10, wherein further comprising a pair ofright-and-left side sills extending in the vehicle longitudinaldirection and provided on both sides, in the vehicle width direction, ofsaid floor tunnel, wherein said side sills are provided at a positionwhich overlaps said first floor cross members and said second floorcross members in a vehicle vertical direction.
 16. The lowervehicle-body structure of claim 15, wherein said upper step portions ofthe vehicle floor contact a lower surface of respective upper faceportions of said first floor cross members in the vehicle verticaldirection.
 17. The lower vehicle-body structure of claim 10, whereinsaid upper step portions of the vehicle floor contact a lower surface ofrespective upper face portions of said first floor cross members in avehicle vertical direction.